Mr Colquhoun has not been seen for almost a month and his family are worried because not only is his absence out of character but he also has bi-polar and is not believed to have any medication with him.

The 26-year-old was last seen on October 12, his brother had a conversation with him at the home they share that afternoon before his best friend saw him about 11pm.

Mr Colquhoun had been having a difficult time, when his brother spoke to him at their Leake Street home in Bayswater but his brother said he felt confident he was okay after their chat.

"I sat down and had a chat with him because I knew that he was feeling a bit down, at the end of the conversation though, I believed that he was happy and it didn't cause me any worry to leave him alone that night," he said.

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"I said I'm always here, I love you, if you need anyone to speak with, I'm here to speak."

His brother spent the night at his girlfriend's house that night and when he returned his brother was not there.

He has had to take time off work because he is finding it difficult dealing with his brother's disappearance.

"I couldn't really function at work," Mr Colquhoun said.

"I'm fearing the worst at the moment.

"I fear for his safety and well being."

His mother Julie Colquhoun said her son had shown no indication that he was planning on going anywhere.

"From what we can tell, everything is still at the home, his toothbrush and all those things that if you were going away even for a couple of days, that you would take with you," she said.

Ms Colquhoun who is from Manjimup, had spent the week prior to her son's disappearance in Perth.

"On Thursday morning, I travelled back to Manjimup and Thursday night he rang me and he seemed fine then, we ended the conversation with 'I love you and see you soon' there was no indication that he was going to disappear," she said.

Ms Colquhoun is worried about her son's well being.

"It's not conceivable to me that he could be looking after himself, especially now that he's got no medication," she said.

"You can't explain how you feel, it's nearly four weeks now and I just need to know he is okay."

Ms Colquhoun made an emotional plea for her son, to get in contact if he could.

"Antony if you are out there, please, please ring and let us know you're okay," she said.

"Please if anyone knows anything about Antony, if you've seen him in the last few weeks, please get in contact with the police."

He is described as having a fair complexion and is 182 centimetres tall with a medium build, brown hair and brown eyes.

He has a distinctive white patch of hair on one side, wears thick black plastic framed glasses and has a tattoo up the top of his right arm.

Mr Colquhoun was wearing an Atari t-shirt the last time he was seen.

Anyone who has information on his whereabouts is asked to call police on 13 14 44.